A diesel particulate filter (DPF) can be damaged during what is known as a ‘drop to idle’ scenario. This is the worst case thermal scenario for a DPF. If an engine of a vehicle drops to idle when the soot combustion process (regeneration process) has just commenced, the maximum potential energy in the form of soot exists in the DPF with the maximum oxygen content seen during engine running but also with the lowest exhaust mass flow to transfer the heat out of the DPF. Additionally, because the vehicle is not moving there is minimal external airflow for cooling the exhaust system from the outside.
Under these conditions the temperature within the DPF can rise to more than 1000° C. and it is possible to crack the DPF, melt the DPF substrate or degrade the catalyst washcoat which is present to aid the removal of other regulated emissions (HC, CO or NOx). In an extreme case this overheating condition can result in the DPF material combusting which can lead to thermal damage of surrounding components.
A temperature that is likely to result in damage to the diesel particulate filer is an unacceptably high temperature and the diesel particulate filter can be considered to be overheating when subject to such a temperature.